Monday, February 20, 2006

The FDA said today that it is closely watching conflicting preliminary data on the risk of thrombosis for women who use the Ortho Evra birth control patch, compared with those who take similar oral contraceptives.

....Interim results of an epidemiologic study indicated that women who use Ortho Evra (norelgestromin/ethinyl estradiol transdermal system) had about a two-fold increased risk for non-fatal venous thromboembolic events compared with women who took a norgestimate-containing oral contraceptive with 35 micrograms of estrogen.

....The data contrast with those of another study, conducted by the Boston Collaborative Drug Surveillance Program, which looked at the risk of heart attack, stroke and venous thromboembolic events in first-time users of the patch.

In this study, published online in the journal Contraception, the authors found that "the risk of nonfatal venous thromboembolic events for the contraceptive patch is similar to the risk for oral contraceptives containing 35 mcg of ethinyl estradiol and norgestimate.

What to make of the conflict? Chances are, the studies are finding very small differences, which would mean that the pill and the patch have comparable risks. As one FDA panel member put it:

For example, it may be that the incidence rates between the two studies are essentially the same, because when one looks at the confidence intervals of the two rates, they overlap. What that simply means is that by chance it's possible that these are telling us the same thing: that the chance of an adverse event with Ortho Evra compared to the comparator contraceptive may in fact be the same.